Yongxiang Chen

Twinning and orientation relationships of T-phase precipitates in an Al matrix

The recent increasing interest of T-phase in Al alloy has been switched to its twins. In this study, we employed high resolution transmission electron microscopy to study and compare the morphology and orientation relationships (OR) of T-phase and its twins in an Al–Cu–Mg–Mn alloy. It is found that T-phase tends to form on the {403}Al habit planes and exhibit a rod-like shape, with it longitudinal axis, [010]T, being parallel to the matrix [010]Al direction. Three different OR types are determined between T-phase and Al matrix, namely, {200}T〈010〉T//{200}Al〈010〉Al (OR-I), {200}T〈010〉T//

Synthesis of single-crystal magnesium-doped spinel lithium manganate and its applications for lithium-ion batteries

{ 40bar{3}}_{text{Al}}

Effect of Mo doping on the structure and electrochemical performances of LiNi 0.6 Co 0.2 Mn 0.2 O 2 cathode material at high cut-off voltage

〈010〉Al (OR-II), and {200}T〈010〉T//{301}Al〈010〉Al (OR-III). OR-II is the most widely observed OR, while OR-I and III can form from the OR-II by twinning. During the twinning, the cross-section of T-phase transforms from a parallelogram-like shape into a shell-like shape. Further analyses on the shell-like T-twins strongly suggest that tenfold twins could form directly from the successive twinning of an individual T crystal.

Modification of LiNi0.5Co0.2Mn0.3O2 cathode material using nano TiO2 to enhance the cycle stability in high-voltage ranges

The chemical lithiated transition metal oxide precursor has been prepared via a hydrothermal process and successfully used for preparing the LiNi0.5Co0.2Mn0.3O2 cathode materials by the post-heat treatment. The results indicate that the lithiated transition metal oxide precursor inherits the morphology of the Ni0.5Co0.2Mn0.3(OH)2 precursor but has a typical α-NaFeO2-type (space group: R-3xa0m) layered structure with an imperfect crystallinity, and the Li is homogenously distributed in the particles. It is further confirmed that the obtained LiNi0.5Co0.2Mn0.3O2 cathode material has a suppressed cation mixing resulting in an excellent electrochemical performance. It delivers the high initial capacity of 187.3xa0mAhg−1 at 1xa0C over the high cutoff voltage range of 3.0–4.6xa0V and the excellent capacity retention of 81.90% after 100 cycles as well as the rate capability of 152.3xa0mAhg−1 at 8xa0C, which are attributed to the low polarization, fast Li+ diffusion and small charge–discharge resistance of the as-prepared material upon cycling.

Enhanced electrochemical performance of Li3PO4 modified Li[Ni0.8Co0.1Mn0.1]O2 cathode material via lithium-reactive coating

Single-crystal magnesium-doped spinel lithium manganate cathode materials are prepared by the hydrothermal method followed by the heat treatment. XRD patterns reveal that Mg2+ions have already diffused into the Li1.088Mn1.912O4 crystal structure and not affect the Fd3m space group. SEM images demonstrate that the magnesium-doped spinel lithium manganates show uniform polyhedral single crystals with 2–4xa0μm. Electrochemical performance demonstrates that the optimized composition of Li1.088Mg0.070Mn1.842O4 electrode exhibits the best electrochemical properties. It delivers 92.0xa0mAhxa0g−1 at 8C rates and corresponds to 90.8% capacity retention (vs. 1C), far higher than those of the pristine electrode (70.4xa0mAhxa0g−1 and 69.2%). In addition, the Li1.088Mg0.070Mn1.842O4 electrode also shows 95.5% capacity retention after 100 cycles at 1C, while the pristine electrode only shows 91.0% capacity retention. The excellent electrochemical performances of Li1.088Mg0.070Mn1.842O4 electrode are ascribed to the suppressed polarization, more stable crystal structure, and better kinetic characteristics.

Enhanced electrochemical properties of the Cd-modified LiNi 0.6 Co 0.2 Mn 0.2 O 2 cathode materials at high cut-off voltage

The lithiated transition metal oxide precursor (LNCMO) with typical α-NaFeO2 structure and imperfect crystallinity, obtained from a hydrothermal process, was pretreated at 500xa0°C and then subjected to sintering at 800–920xa0°C to synthesize the ternary layered LiNi0.5Co0.2Mn0.3O2 (NCM523). X-ray diffraction (XRD), scanning electron microscope (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge/discharge testing were used for investigating the effect of the high-temperature crystallization on the properties of the NCM523 cathode materials. The results show that the materials heated at 880–900xa0°C possess superior cation ordering, perfect crystallinity, and excellent electrochemical performances, among which the material heated at 900xa0°C delivers better performances, with the initial discharge capacity of 152.6xa0mAhxa0g−1 at 0.5 C over 3.0 to 4.3xa0V and the capacity retention of 95.5% after 50xa0cycles. Furthermore, the effect of the high-temperature crystallization on the Li+ diffusion coefficient, potential polarization, and electrochemical resistance are discussed.